Process for impregnating wood and products thereof



3,519,476 PROCESS FOR IMPREGNATING WOOD AND PRODUCTS THEREOF Bart J. Bremmer and Lawrence F. Sonnabend, Midland,

Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Filed Nov. 22, 1967, Ser. No. 684,955 Int. Cl. C09d /18; B27k 3/50 U.S. Cl. 117136 Claims ABSTRACT OF THE DISCLOSURE A process for impregnating wood with a dimensionally stabilizing and fire-retardant resin which comprises: (1) reacting a mixture of a phenol and NH urea or an amine with an aldehyde, and then adding an acid to that reaction mixture; (2) impregnating the wood with the above product; and (3) contacting the impregnated wood with heat alone, or heat and an excess of NH or an amine to cure the resin.

BACKGROUND OF THE INVENTION In normal practice, the fire-retardant qualities of wood are improved by the addition of a salt to the wood. This process, however, results in a composition from which the fire-retardant chemical is easily removed 'under high humidity or wet conditions.

This invention is an improvement of, and diifers from, the prior art in that the fire-retardant additives are formed in, and/ or impregnated into, the wood. Thus, they are not readily extracted. Moreover, the impregnation of the wood with the resin, and its subsequent curing, results in dimensional stability.

SUMMARY OF THE INVENTION This invention is a novel process for dimensionally stabilizing and improving the fire-retardancy of wood, which comprises impregnating said wood with a phenol/ aldehyde/amine resin-acid composition, which is water soluble, and then cross-linking the resin with heat alone, or heat and NH or an amine, at elevated temperatures. The resulting cured resin is not water soluble and the qualities imparted to the wood by it, i.e. dimensional stability and improved fire-retardancy, are not, therefore, dimensioned by leaching during periods of wetness or high humidity.

More particularly, the instant invention is a process which comprises reacting by contacting, at a temperature of about 25 to 80 C., and preferably about 45 to 55 C., a mixture of about 1 mole of a phenol having at least two reactive hydrogen sites in the ortho and/ or para positions of the benzene ring, and about 0.2 to 1.0 mole, preferably about 0.3 to 0.6 mole, of either NH urea or an aliphatic or cycloaliphatic amine having at least two active hydrogen sites on the amine nitrogen or nitrogens, with about 1 to 5 moles, preferably about 1.2 to 2 moles, of an aliphatic or cycloaliphatic aldehyde. After the above reactants have had ample time to react, suitably about one-half to one and one-half hours, an acid which contains one or more of the elements B, P, Cl, As, Br, Sb and I, such as H PO HCl, H BO HBr, H SbO HI, trichloroacetic acid, diiodoacetic acid, and arsenoacetic acid, or mixtures of said acids is added to produce the fire-retard- 3,519,476 Patented July 7, 1970 ant qualities desired. Concentrations of said acids or mixtures thereof is not critical.

The phenols which are suitable for the process of this invention can be substituted with inert substituents in any available ring position, suitable substituents being, for example, halogenated phenols, such as 3-chlorophenol, 4-bromophenol, 2,5-dichlorophenol and 3,5-di brornophenol; alkyl phenols of from 1 to 8 carbon atoms in each alkyl group, such as 3-propylphenol, S-methylphenol, 3,5-dimethylphenol, 3-methyl-5-0ctylphenol and 3,5-diethyl-4-methylphenol.

The aldehydes which are suitable for the process of this invention are aliphatic and cycloaliphatic aldehydes of from 1 to 5 carbon atoms, such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde and furfuraldehyde.

The amount of acid, or mixtures thereof, used for this process is generally any amount which represents a desired level of protection from fire or prolonged heat.

Suitably, about 0.1 to 2.0 moles per mole of phenol and more may be employed, with the exception of H BO for which an upper limit of 0.25 mole per mole of phenol is desirable, as an amount in excess of this will crystallize out of solution.

The product prepared according to the above is water soluble, and is impregnated into wood through any standard method, such as soaking, pressure or vacuum techmques.

The material to be treated with the process of this invention can suitably be planks, boards, shingles or any other split, sawed or planed wood or lumber product, or any material made from the molding or forming, by any technique, of ground, shredded, splintered or otherwise cut-up pieces of wood.

The amount of the above product which is absorbed by wood, i.e., percent pickup weight, is defined as the weight of product absorbed by the sample (calculated by subtracting the samples dry weight from the samples weight after impregnation), divided by the weight of the sample before impregnation, times 100. The product of this process lends itself to a wide range of efiective percent pickup weights. Generally, the pickup will vary according to the following factors: quality desired, i.e., dimensional stability or fire-retardancy; degree of that quality sought; type of acid and amount used; and material to be treated. Evaluation by standard tests, well known in the art, for dimensional stability and fire retardancy will teach the optimum amount to be used in a given case. Generally, about 10% to about or more, is suitable for most materials.

After the material has absorbed the desired percent pickup weight, it is then cured. Curing can be accomplished in three ways: (1) heat the impregnated material to about 85 to C., or (2) treat the impregnated material with NH or a liquid or gaseous aliphatic or cycloaliphatic primary or secondary amine (a) while heating to 85 to 150 C., or (b) heat the impregnated material to 85 -150 C. after said treatment. Primary and secondary amines which are suitable for the process of this invention are those which contain 1 to 16 total carbon atoms, for example, monomethylamine, t-butylamine, tri-n-butylamine and ethylenediamine, dioctyldiamine, piperidine, cyclohexylamine, and dibutylamine.

Suitably an excess, based on the equivalents of acid originally employed, of the curing agent is employed,

3 and, for practical purposes, no less than about one equivalent of said agent per equivalent of acid originally employed should be used. Although atmospheric or autogenous pressure is suitable, pressures of 50 to 200 p.s.i.g. are desirable to shorten the curing process and At The fire retardant qualities of treated Ponderosa pine were further tested by the so-called crib test, ASTM designation E160-50. Table II, following, summarizes these data. The first column, i.e. Run No., gives the impregnation solution tested, the numbers corresponding insure greater contact of resin and curing agent. to Table T run nu red 1+2 is a 50%50% The resin-like product of the first art of this process mixture of these two individual products, as is the run is not normally suitable as a glue for making pressu red +4 a 50%50% mixtu e f th se tW board, wallboard and other wood materials which are The column labeled Flame Out indicates, in terms molded or formed from pieces of wood. However, it does of minutes and seconds, when the flame went out in the ofier dimensional stability and fire-retardancy for these samples in relation to when the burner Was applied. types of products when incorporated into the materials Please note that the ASTM requires the burner to be apin, for example, these two ways: plied to the wood for only 3 minutes.

(1) Impregnate and crosslink the finished product in Finally, the last column indicates the average percent the same way boards, shingles, etc, would be treated; pickup weight of the samples, said term being previously (2) Impregnate and crosslink each individual piece defined. of wood before they are glued together into the finished product. TABLE H SPECIFIC EMBODIMENTS 90 iii iv i ii 5355' -asst A number of samples were made using the process of H I I, this invention, each sample varying from the others only 5,53 33:; fig 3% in the kind and amount of acid used. 1 62.6 N 4428 In all cases, 3 moles (282 grams) of phenol and an gig gig 12:3 amine (compound and amount specified in following 89.7 .--do 45.0 chart) were placed in a suitable vessel and heated to 50 C. Then, 4 moles (325 grams) of 37% formaldehyde We claim: were added over a -minute period while keeping the 1. A process for impregnating wood With a fire-retemperature at 50 C. The reaction mixture was kept at tardent resin, which comprises: this temperature for an additional one and one-half 30 (A) Reacting by contacting a mixture of hours and then cooled to 25 C. 1 mole of a phenol having at least two reactive At this point various kinds and amounts of acids were hydrogen sites in the ortho and para positions added, under stirring, as follows: of the benzene ring, and

TABLE I Amine used HgPO-t HBr 11 B 0 Run number Grams Moles Grams Moles Grams Moles Grams Moles Monoethanolamine:

The products which resulted were clear and water 0.2 to 1.0 mole of NH urea or an aliphatic or soluble. cycloaliphatic amine having at least two re- For the treatment of wood with the above products, active hydrogen sites on the amine nitrogen or the following general procedure was followed: nitrogens, with Pieces of Ponderosa pine with dimensions /2 inch x /2 1 to 5 moles of an aliphatic or cycloaliphatic inch X 3 inches were impregnated with various samples, 50 aldehyde containing not more than 5 carbon and mixtures thereof, of the products as defined in atoms, and then adding Table I by placing the pieces of wood in a one-liter an amount of an acid containing one or more of Parr bomb and drawing a vacuum on the bomb. The the elements B, P, Cl, As, Br, Sb and I, or product was then added under vacuum, the vacuum remixtures of said acids, suflicient to produce the leased and the wood soaked in it for 30 minutes. The desired fire-retardant effect; excess was then drained and ammonia gas put in the (B) Impregnating the wood with the product of (A) bomb until a pressure of 10 p.s.i.g. was obtained. The above with a percent pickup weight sufficient to contents of the bomb were then heated to 100 C. and impart the desired fire-retardancy; and a pressure of 70 p.s.i.g. applied using nitrogen gas. The (C) Curing the impregnated wood. wood pieces were kept at 100 C. overnight, removed 2. The product produced by the process of claim 1. from the bomb and dried at 90 to 95 C. until the weight 3. The process of claim 1 wherein the mole ratio of of the pieces remained constant. phenol/ amine is 1.0/ 0.3 to 1.0/ 0.6.

Pieces of pine treated with each of the products of 4. The process of claim 1 wherein the phenol used Table I were then held in the flame of a Bunsen burner. is phenol. They did not burn after the flame was removed, nor was 5. The process of claim 1 wherein the amine used in there any significant afterglow. step (A) is ethanolamine or ethylenediamine.

Samples of wood-fiber pressboard were similarly, im- 6. The process of claim 1 wherein the acid used is pregnated with each of the products of Table I, the per- H PO HBr, H BO or a mixture thereof. cent pickup weight varying from 6.8% to 63% by vary- 7. The process of claim 1 wherein the amount of acid, ing the soak time. This material when held in the flame or mixture of acids, used is 0.1 to 2.0 moles per mole of a Bunsen burner did not burn after the flame was of phenol, removed when the impregnation was above 9.4% pickup 8. The process of claim 1 wherein the percent weight Weight. Below this percent, the material did not burn pickup is 10% to 120%. as severely as a non-treated sample, however. The after- 9. The process of claim 1 wherein the curing agent used in step (C) is NH glow was also considerably less.

References Cited UNITED STATES PATENTS 5 Groebe 106-15 X Eckert 106-15 X Nason et a1. 117-137 X Boiney 117-136 X Golstein et a1 106-15 X 10 Anderson 117-148 Golstein et a1. 117-137 6 Golstein et a1. 117-137 X Fitko et a1. 117-161 X Smith 117-148 X Sunden 117-137 X Guth 1l762.2

US. Cl. X.R. 

